1. Field of the Invention
The present invention is generally related to a marine transmission and, more particularly, to a marine transmission in which a driving shaft and a driven shaft are aligned coaxially for transfer of torque directly through a cone clutch.
2. Description of the Prior Art
Those skilled in the art of marine propulsion systems are aware of many different types of transmissions that are used to provide the ability to allow the marine propulsion system to be operated in forward, neutral, and reverse gear positions. Some of these transmissions are located in the drive unit of a sterndrive marine propulsion system. Other types of transmissions are located between an engine, within the bilge of a marine vessel, and the transom of the marine vessel.
U.S. Pat. No. 3,608,684, which issued to Shimanckas on Sep. 28, 1971, describes a clutch for a marine propulsion device. The device affords reverse operation by rotation of the drive shaft housing about a vertical axis. It includes a clutch in the lower unit gear case for selectively engaging or disengaging the propeller shaft with the drive shaft. The clutch is responsive to axial movement of the drive shaft caused by moving a control handle accessible to the operator.
U.S. Pat. No. 3,842,788, which issued to Kroll on Oct. 22, 1974, describes a reversible transmission. The device includes a reversible clutch or transmission which includes a pair of facing drive gears rotatably mounted on a propeller shaft and having drive lugs, a shiftable driver mounted to the propeller shaft between the drive gears for axial movement relative to and in common rotation with the propeller shaft, a pair of clutch dogs rotatably carried on the propeller shaft driver and having drive lugs which are drivingly engageable with drive lugs on the corresponding drive gears, and means for selectively shifting the propeller shaft driver axially on the propeller shaft to drivingly engage a clutch dog with the corresponding drive gear.
U.S. Pat. No. 3,919,964, which issued to Hagen on Nov. 18, 1975, describes a marine propulsion reversing transmission with hydraulic assist. The device comprises a reversing transmission located in a propulsion unit and connecting a drive shaft to a propeller shaft and shiftable between neutral, forward drive, and rearward drive conditions, together with a mechanical linkage extending in the propulsion unit and connecting to the reversing transmission for operating the reversing transmission in response to movement of the mechanical linkage. It also comprises a hydraulic arrangement actuated in response to initial movement of the mechanical linkage for assisting in moving the mechanical linkage to operate the reversing transmission.
U.S. Pat. No. 3,943,790, which issued to Meyer on Mar. 16, 1976, discloses a marine outboard gear assembly. It features a constant drive of the meshing gears which transfer powers to the propeller-shaft axis and a selective spring-clutching direct to the propeller shaft. It utilizes the meshing gears for lubricant circulation as long as the engine is operating and whether or not the clutch is engaged and it reduces, to an absolute minimum, the drag and inertial effects operative upon the propeller shaft when the boat is moving in the declutched condition.
U.S. Pat. No. 4,244,454, which issued to Bankstahl on Jan. 13, 1981, discloses a cone clutch. The cone clutch has its forward and reverse clutch gears supported by bearings mounted on the housing with a main shaft supported by bearings mounted on the housing in the same planes as the forward and reverse gear bearings. The male cone member is biased by two springs, each encircling cam faces on the member and bearing against the forward and reverse clutch gears, respectively, to bias the cone member away from its center or neutral position.
U.S. Pat. No. 4,257,506, which issued to Bankstahl on Mar. 24, 1981, discloses a shifter linkage for a cone clutch. The male cone member of a cone clutch mechanism has two springs, each encircling cam faces on the male cone member and bearing against the forward and reverse clutch gears, respectively, to bias the cone member away from its center or neutral position toward either the forward or reverse clutch gear. An eccentric roller on the shift actuator shaft engages with a circumferential groove in the male cone member to provide a vibrating force against the member for shifting.
U.S. Pat. No. 4,397,198, which issued to Borgersen et al. on Aug. 9, 1983, describes a marine transmission assembly system. A reversing double cone clutch drive assembly for a boat comprising a horizontal input shaft, a vertical intermediate output shaft, a first housing provided with an opening in a side wall opposite to the input shaft and an opening in a bottom wall through which the lower end of the intermediate output shaft is exposed, and selectable gear transmission subassemblies attachable to the clutch drive assembly are described. Each subassembly includes a second housing with a generally horizontal wall for engaging the bottom wall, the second housing carrying a bearing which mounts on an output shaft driven through gear means by the intermediate output shaft.
U.S. Pat. No. 4,630,719, which issued to McCormick on Dec. 23, 1986, discloses a torque aided pulsed impact shift mechanism. A cone clutch sleeve on a main shaft is moved axially between forward and reverse counter rotating gears by a yoke having mirror image oppositely tapered cams on opposite sides thereof which are selectively rotatable to engage eccentric rings on the forward and reverse gears. This engagement drives the yoke away from the one engaged gear and toward the other gear to, in turn, drive the clutch sleeve out of engagement with the one gear such that torque applied through the cam engaged gear ring assists clutch disengagement.
U.S. Pat. No. 5,072,629, which issued to Hirukawa et al. on Dec. 17, 1991, describes a shift assisting system. The mechanism for assisting the shifting of a dog clutch of a marine transmission by reducing the engine speed is described. The requirement for engine speed reduction is sensed by a pressure sensitive conductive rubber type pressure sensing switch contained within the inner connection between the operator and the dog clutch.
U.S. Pat. No. 5,509,863, which issued to Mansson et al. on Apr. 23, 1996, describes a transmission device for boat motors. The transmission comprises an input shaft, a reversing mechanism and an output shaft. The reversing mechanism is comprised by a right angle bevel gearing with two bevel gears, which are freely rotatably mounted on an intermediate shaft and engaged with a bevel gear on the input shaft. The bevel gears each cooperate with an individual clutch respectively, by which one of the bevel gears can be locked to the intermediate shaft. The clutches are placed outside the bevel gearing. The clutches are wet clutches compressible by a piston that moves in a cylinder which in turn communicates with a hydraulic pump driven by one of the input and intermediate shafts.
U.S. Pat. No. 5,709,128, which issued to Skyman on Jan. 20, 1998, describes reversing gears for boats. A reversing gear for boats, comprising a displaceable engagement sleeve with a V-shaped groove is described. There extends a gear selector into the V-shaped groove in the form of a dog on a pin moveable in the axial direction of the engaging sleeve. The pin is eccentrically mounted in a rotatable sleeve. A ball and socket joint between the dog and the pin assures that the dog will retain its orientation and contact surface in the groove during the shifting movement.
U.S. Pat. No. 5,890,938, which issued to Eick et al. on Apr. 6, 1999, discloses a marine counter rotational propulsion system. A system with counter rotating propellers is provided with the capability of causing the propellers to rotate at different speeds. A first gear is attached to an inner propeller shaft and a second gear is attached to an outer propeller shaft. The inner and outer propeller shafts are arranged in coaxial and concentric relation for rotation about an axis of rotation. A drive shaft is connected to a pinion gear which engages the teeth of the fore and aft gears at different effective diameters. The pinion gear meshes with a first plurality of gear teeth on a beveled surface of the fore gear while a second set of gear teeth of the pinion gear mesh with a second plurality of gear teeth on a beveled surface of the aft gear. Because of the different effective diameters of the first and second pluralities of gear teeth, the inner and outer shafts rotate at different speeds.
U.S. Pat. No. 6,062,360, which issued to Shields on May 16, 2000, discloses a synchronizer for a gear shift mechanism for a marine propulsion system. A synchronized gear shift mechanism is provided for a marine propulsion system. Using a hub and a sleeve that are axially moveable relative to an output shaft but rotationally fixed to the shaft and to each other, the gear shift mechanism uses associated friction surfaces to bring the output shaft up to a speed that is in synchronism with the selected forward or reverse gear prior to mating associated gear tooth surfaces together to transmit torque from an input shaft to an output shaft. The friction surfaces on the forward and reverse gears can be replaceable to facilitate repair after the friction surfaces experience wear.
U.S. Pat. No. 6,523,655, which issued to Behara on Feb. 25, 2003, discloses a shift linkage for a marine drive unit. The linkage is provided with a groove that is aligned along a path which is nonperpendicular to an axis of rotation of the shift linkage. The groove, and its nonperpendicularity to the axis of rotation, allow a detent ball to smoothly roll or slide along the groove. This relationship helps to maintain the shift linkage in a desired vertical position as it passes from one gear selection position to another.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Most current sterndrive systems use a transmission to shift between forward, neutral, and reverse gears in one of four basic ways. A complete hydraulic clutch pack style of transmission utilizes a planetary gear set for reverse. This type is mounted directly to the engine in front of the sterndrive U-joint. It tends to be inefficient due to the use of a hydraulic pump, clutch packs, and the losses of the large planetary assembly structure. This type of transmission also tends to be relatively large and requires more space in a marine vessel than that which is typically available in many types of boats.
Another style of transmission is intentionally designed to be shifted only when the engine is inactive. This type typically uses a dog clutch and is used primarily for racing applications.
A cone clutch style of transmission is usually built into the upper drive shaft housing of a sterndrive system. They typically have an input pinion meshing with two gears, one above and one below the center line of the input pinion rotation, which rotates about the vertical drive shaft axis. These gears are rotated in opposite directions and a cone clutch engages one gear or the other to achieve forward or reverse gear selection. Full engine power is transmitted through one of the gear sets at all times that the engine is operating. The requirements of the gears are typically high because of the loading cycle that they must handle. Ideally, the gear geometry could be optimized, but the requirement that the cone clutch be mounted between the two driven gears limits this optimization.
Another type of transmission that is often used is typically located in the gear case. It is similar in function to the cone clutch, except that a dog clutch is used, and it is located for axial movement on the propeller shaft. A pinion drives two gears at all times. These gears are located on the propeller shaft and rotate in opposite directions. Forward and reverse gear positions are achieved by engaging the dog clutch to one gear or the other. The teeth of the dog clutch must be aligned before it can be engaged. When the mating components are spinning at different speeds, this can lead to excessive noise until the teeth actually engage with each other.
When cone clutches are used, as described above, they are typically contained in the drive shaft housing. All of the power from the engine is transmitted through a pinion gear to the forward and reverse gears which must run constantly because of their constant mesh with the pinion gear. These applications typically maintain an oil level in the transmission that submerges the mesh of at least one gear.
It would be significantly beneficial if torque could be transmitted from a driving shaft to a driven shaft, in forward gear, without having to transmit torque through meshed pinion and bevel gears. It would also be significantly beneficial if the gear meshes were not constantly submerged in gear oil. These features would improve operating efficiency and reduce the amount of heat generated by the transmission. In addition, these features would also allow the transmission to be more compact than known transmissions.